U.S. patent number 4,527,428 [Application Number 06/442,665] was granted by the patent office on 1985-07-09 for semiconductor pressure transducer.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Shigeyuki Kobori, Motohisa Nishihara, Satoshi Shimada, Seikou Suzuki, Kazuji Yamada.
United States Patent |
4,527,428 |
Shimada , et al. |
July 9, 1985 |
Semiconductor pressure transducer
Abstract
A semiconductor pressure transducer including a measuring
diaphragm of semiconductor material for sensing pressure supported
by a support member of the same material. An oxide layer and a thin
glass layer are interposed between the measuring diaphragm and the
support member.
Inventors: |
Shimada; Satoshi (Hitachi,
JP), Yamada; Kazuji (Hitachi, JP), Suzuki;
Seikou (Hitachiota, JP), Kobori; Shigeyuki
(Hitachi, JP), Nishihara; Motohisa (Katsuta,
JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
23757651 |
Appl.
No.: |
06/442,665 |
Filed: |
December 30, 1982 |
Current U.S.
Class: |
73/721; 338/4;
73/706; 73/718 |
Current CPC
Class: |
G01L
9/0054 (20130101); G01L 13/025 (20130101); G01L
19/147 (20130101); G01L 19/0645 (20130101); G01L
19/0038 (20130101) |
Current International
Class: |
G01L
9/00 (20060101); G01L 13/00 (20060101); G01L
13/02 (20060101); G01L 009/06 () |
Field of
Search: |
;73/727,718,706,721,724,DIG.4 ;338/2,4,5 ;357/40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Woodiel; Donald O.
Attorney, Agent or Firm: Antonelli, Terry & Wands
Claims
What is claimed is:
1. A semiconductor pressure transducer comprising:
a measuring diaphragm formed of semiconductor material;
a support member formed of semiconductor material for supporting
said measuring diaphragm;
an oxide layer having a high affinity to glass and a thin glass
layer interposed between said measuring diaphragm and said support
member, said oxide layer enabling said thin glass layer of uniform
thickness to be formed, said measuring diaphragm and said support
member being joined to each other by anodic bonding through said
thin glass layer;
a main body on which said support member is mounted; and
means located in said main body for applying pressures of fluids to
be measured to said measuring diaphragm.
2. A semiconductor pressure transducer as claimed in claim 1,
wherein said oxide layer is located on said support member.
3. A semiconductor pressure transducer as claimed in claim 2,
wherein said thin glass layer is located on said oxide layer.
4. A semiconductor pressure transducer as claimed in claim 3,
wherein said thin glass layer is formed by sputtering.
5. A semiconductor pressure transducer as claimed in claim 3,
wherein said thin glass layer has a thickness below 10 .mu.m.
6. A semiconductor pressure transducer as claimed in claim 1,
wherein said support member and said measuring diaphragm are made
of the same semiconductor material.
7. A semiconductor pressure transducer as claimed in claim 6,
wherein said same semiconductor material is silicon.
8. A semiconductor pressure transducer as claimed in claim 7,
wherein the thin glass layer is of a borosilicate glass.
9. A semiconductor pressure transducer as claimed in claim 1,
wherein the oxide layer is located on the measuring diaphragm.
10. A semiconductor pressure transducer as claimed in claim 1,
wherein said oxide layer has a thickness in the range between 0.1
and 1 .mu.m.
11. A semiconductor pressure transducer comprising:
a pressure sensing section main body having introduced thereinto
two fluids of different pressures to be measured;
a measuring diaphragm of semiconductor material, provided in said
pressure sensing section main body, including a large thickness
portion, a small thickness portion formed with piezo resistance
elements located outside said large thickness portion and a fixed
portion of large thickness located outside said small thickness
portion;
a support member of semiconductor material joined to said fixed
portion of said measuring diaphragm through an oxide layer having a
high affinity to glass and a thin glass layer by anodic bonding,
said oxide layer enabling said thin glass layer of uniform
thickness to be achieved;
pressure passageways for fluids formed in said support member;
and
means for applying pressures of said two fluids to be measured to
opposite side surfaces of said measuring diaphragm.
12. A semiconductor pressure transducer as claimed in claim 11,
wherein the crystal surface of said measuring diaphragm is a {100}
surface and said piezo resistance elements are arranged parallel to
a <110> axis.
13. A semiconductor pressure transducer as claimed in claim 11,
further comprising a support member of metal interposed between
said support member and said main body.
14. A semiconductor pressure transducer as claimed in claim 13
wherein said support member of metal is formed of an alloy selected
from the group consisting of an Fe-Ni alloy and an Fe-Ni-Co
alloy.
15. A semiconductor pressure transducer comprising:
a pressure receiving section main body;
two seal diaphragms each located on either side of said pressure
receiving section main body for defining a high pressure fluid
receiving chamber and a low pressure fluid receiving chamber;
a center diaphragm arranged in said pressure receiving section main
body to define two separation chambers each communicating with one
of said pressure receiving chambers;
a measuring diaphragm of semiconductor material formed with piezo
resistance elements on one surface thereof and formed with a large
thickness central portion, a large thickness outer peripheral
portion and a small thickness portion interposed between said
central portion and said outer peripheral portion;
a support member of semiconductor material having a pressure
passageway connected at one end to a peripheral portion of the
other surface of said measuring diaphragm by anodic bonding through
a thin glass layer and an oxide layer having a high affinity to
glass, said oxide layer enabling said thin glass layer of uniform
thickness to be obtained;
a support member of metal having a pressure passageway connected at
one end to the other end of said support member of semiconductor
material and communicated with said pressure passageway of said
support member of semiconductor material;
a pressure sensing section main body connected to the other end of
said connecting member of metal;
a connecting metal member having a first pressure passageway
communicating said the other surface of said measuring diaphragm
with one of said pressure receiving chambers through the support
members of semiconductor material and metal, and a second pressure
passageway communicating said one surface of said measuring
diaphragm with the other pressure receiving chamber; and
a noncompressive fluid sealed in said pressure receiving chambers,
separation chambers and first and second pressure passageways.
16. A semiconductor pressure transducer comprising:
a measuring diaphragm of semiconductor material;
a support member of semiconductor material cooperating with said
measuring diaphragm to define measuring chambers therebetween;
an oxide layer having a high affinity to glass and a thin glass
layer interposed between said measuring diaphragm and support
member, said support member being joined to said measuring
diaphragm by anodic bonding, said oxide layer enabling said thin
glass layer of uniform thickness to be obtained;
a main body having said support member mounted thereon;
pressure passageways formed in said main body for leading fluids to
be measured to said measuring chambers; and
means for sensing changes in electrostatic capacity between said
measuring diaphragm and said support member.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a semiconductor pressure transducer using
a measuring diaphragm of semiconductor material for converting a
fluid pressure into an electric signal.
(2) Description of the Prior Art
In one type of measuring diaphragm of semiconductor, such as Si,
used for sensing pressure known in the art, the measuring diaphragm
includes, as described in U.S. Pat. No. 4,303,903, a central
portion of small thickness constituting a distortion generating
section and an outer peripheral portion of large thickness and has
piezo resistor elements located at the distortion generating
section to have changes in resistance sensed. In another type of
measuring diaphragm of semiconductor, changes in electrostiatic
capacity between it and another fixed electrode are measured, as
described in U.S. Pat. No. 4,247,274.
Such measuring diaphragm is mounted on a main body by a support
member. In view of the ease with which bonding of the measuring
diaphragm to the support member can be effected and also by taking
into consideration the need to insulate the measuring diaphragm
from the main body, it is considered desirable that the support
member should be formed of glass (preferably borosilicate glass to
obtain agreement in the coefficient of thermal expansion) and the
anodic bonding disclosed in U.S. Pat. No. 3,397,278 should be used
to effect bonding.
Meanwhile a measuring diaphragm formed of Si and a support member
formed of glass are substantially equal to each other in the
coefficient of thermal expansion, but they are distinct from each
other in Young's modulus of elasticity. The difference in Young's
modulus of elasticity should pose no serious problem when the
pressure of a fluid to be measured is relatively low. However, when
a line pressure (hydrostatic pressure) of over 100 kg/cm.sup.2 is
applied, the measuring diaphragm and the support member show a
variation in deformation caused by the hydrostatic pressure, so
that an output is produced by the hydrostatic pressure and errors
tend to occur in the measurements.
SUMMARY OF THE INVENTION
To obviate the aforesaid problem of the prior art, attempts have
been made to form a thin layer of glass interposed between the
measuring diaphragm and a support member formed of Si so that the
support member is essentially formed of Si. However, it has been
found that great difficulties are encountered in producing a thin
film of uniform thickness on the order of several .mu.m. Efforts
have been made in directly forming a thin layer of glass by
sputtering on the measuring diaphragm of Si or the support member
of Si but no thin layer of glass of uniform thickness has ever been
formed.
Accordingly this invention has as its object the provision of a
semiconductor pressure transducer capable of forming a thin film of
glass between the measuring diaphragm and the support member with
ease which is difficultly influenced by hydrostatic pressure.
The outstanding characteristic of the invention is that the
measuring diaphragm and the support member are formed of
semiconductor of the same material, such as Si, and a film of oxide
is formed on the surface of the measuring diaphragm or support
member on which a thin layer of glass is provided by sputtering or
chemical vapor deposition (CVD), with the measuring diaphragm being
joined to the support member by anodic bondng in such a manner that
the thin layer of glass is interposed between them.
Such film of oxide has the function of an insulating layer like
glass, and since the main component of glass is SiO.sub.2, the film
of oxide has good affinity with glass and a thin layer of glass of
uniform thickness can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of the pressure transducer comprising
one embodiment of this invention, showing its construction in its
entirety.
FIG. 2 is a sectional view of the pressure sensing section of the
pressure transducer shown in FIG. 1, showing its construction in
detail;
FIG. 3A is a top plan view of the measuring diaphragm, showing some
portions thereof in detail;
FIG. 3B is a sectional view of the measuring diaphragm shown in
FIG. 3A;
FIG. 4 is a diagram showing the relation between temperature and
output voltage; and
FIG. 5 is a sectional view of the pressure transducer of the
electrostatic capacity in which the invention is incorporated,
showing the construction thereof in its entirety.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a sectional view of the pressure transducer comprising
one embodiment of the invention, showing its construction in its
entirety. The pressure transducer comprises a pressure receiving
section 10 and a pressure sensing section 12. The pressure
receiving section 10 includes a main body 14 having a high pressure
side pressure receiving diaphragm 16 and a low pressure side
pressure receiving diaphragm 18 of stainless steel which may be
Monel metal, hastelloy or tantalum when the fluid handled is highly
corrosive joined thereto by welding on its sides, to define a high
pressure side pressure receiving chamber 20 and a low pressure side
pressure receiving chamber 22 between the pressure receiving
section main body 14 and the high pressure side pressure receiving
diaphragms 16 and the low pressure side pressure receiving
diaphragm 18 respectively. A center diaphragm 24 of stainless steel
higher in stiffness than the stainless steel forming the high and
low pressure side pressure receiving diaphragms 16 and 18 is joined
by welding to the central portion of the pressure receiving section
main body 14 to define between it and the pressure receiving
section main body 14 a high pressure side separation chamber 26 and
a low pressure side separation chamber 28. The high pressure side
pressure receiving chamber 20 is maintained in communication with
the high pressure side separation chamber 28 through a pressure
conduit 32 having a throttle 30, and the low pressure side pressure
receiving chamber 22 and the low pressure side separation chamber
28 are maintained in communication with each other through a
pressure passageway 34. The pressure receiving section main body 14
is formed with pressure passageways 36 and 38 for communicating the
high pressure side separation chamber 26 and low pressure side
separation chamber 28 respectively with the pressure sensing
section 12, and with ports 40 and 42 for introducing noncompressive
liquid, such as silicon oil, therethrough into the pressure
receiving section 10 and pressure sensing section 12 to be sealed
therein. A high pressure side flange 46 formed with a high pressure
fluid inlet port 44 and a low pressure side flange 50 formed with a
low pressure fluid inlet port 48 are secured to the pressure
receiving section main body 14 by bolts 52 and nuts 54 near four
corners at opposite sides thereof in a manner to enclose the high
pressure side seal diaphragm 16 and low pressure side seal
diaphragm 18.
The pressure sensing section 12 includes a measuring diaphragm 56
formed of n-type single crystal silicon of {100} face located
substantially in the central portion. As shown in FIGS. 2, 3A and
3B, the measuring diaphragm 56 includes a large thickness central
portion 58, a large thickness outer peripheral portion 60 and a
small thickness portion 62 formed as a groove interposed between
the central portion 58 and the outer peripheral portion 60. The
large thickness portions 58 and 60 each have a thickness 0.35 mm
and the outer peripheral portion is square in shape and has sides
in the range between 3 and 9 mm. The small thickness portion 62 has
a straight line portion in which P-type piezo resistance elements
64, 66, 68 and 70 are arranged. Anisotropic etching may be relied
on by using an alkaline solution, such as KOH, to obtain the small
thickness portion 62 of the shape described. The thickness of the
small thickness portion 62 may vary depending on the range of the
pressure differentials to be measured and output sensitivity, for
example. The ratio of the small thickness portion 62 to the outer
diameter thereof is of importance from the point of view of
obtaining accurate measurements and such ratio should be over
0.5.
The piezo resistance elements 64-70 are formed by selective
diffusion of impurities two each on the surface of the measuring
diaphragm 60 in the vicinity of the large thickness outer
peripheral portion 60 and the large thickness central portion 58 in
such a manner that they are in bridge connection. Four sets of such
bridge are provided to the surface of the small thickness portion
62 and one of them is selectively used. The piezo resistance
elements 64-70 each include four fine series with one another by a
low resistance layer in such a manner that they have their
<110> axis or their maximum piezo sensitivity axis in the
{100} face in alignment with their length. Formed on the surface of
the large thickness outer peripheral portion 60 serving as a fixed
portion are three temperature sensitive elements 72, 74 and 76
which play an effective role in effecting temperature
characteristic compensation when the ranges of the pressure
transducer are switched. The temperature sensitive elements 72-76
each include two stringlike members parallel to each other
connected in series with each other by a low resistance layer in
such a manner that they have their <100> axis of
substantially zero piezo sensitivity in alignment with their
length. A pad 78 imparts the highest potential to a Si diaphragm
base plate to effectively avoid influences which might otherwise be
exerted by induced noises. Conductors 80 are formed by vaporization
deposition of Al to connect the elements together. An electrode pad
82 is also formed by vaporization deposition of Al.
The measuring diaphragm 56 extends outwardly of a pressure sensing
section main body 92 of stainless steel through a first support
member 88 having a thin glass layer 84 and an oxide layer 86 and a
second support member 90 of metal. The first support member 88 is
formed of Si like the measuring diaphragm 56 and the oxide layer 86
thereon has a thickness in the range between 0.1 and 1 .mu.m. The
thin glass layer 84 is formed by sputtering in a thickness ranging
from 1 to 5 .mu.m. The thickness of the thin glass layer 84 is
preferably small. However, when it is below 10 .mu.m, no trouble
occurs in practical use. The glass for forming the thin glass layer
84 is preferably borosilicate glass having substantially the same
coefficient of thermal expansion (3.125.times.10.sup.-5
/.degree.C.) as Si. When the thin glass layer 84 is formed by CVD,
it is necessary to subject the thin glass layer to heat treatment
to obtain hardening thereof. The second support member 90 is formed
of Fe-Ni (40%) alloy (3.6.times. 10.sup.-6 /.degree.C.) or Fe-Ni
(30%)-Co (17%) alloy (5.4.times.10.sup.-6 /.degree.C.) having
substantially the same coefficient of thermal expansion as Si. The
measuring diaphragm 56 is joined to the first support member 88
having the thin glass layer by anodic bonding and the first and
second support members 88 and 90 are joined to each other by an
organic adhesive agent or Au-Si eutectic alloy while the second
support member 90 is joined to the pressure sensing section main
body 92 by arc welding.
The oxide layer 86 formed on the first support member 88 ensures
that the measuring diaphragm 56 formed of Si is highly insulating.
That is, when pinholes develop in the thin glass layer 84 formed on
the oxide layer 86, the latter performs the function of insulation
and positively performs the function of insulation at elevated
temperature. Since the main component of the thin glass layer 84 is
SiO.sub.2, it has high affinity with the oxide layer 86 and the
glass layer 84 can be made uniform in thickness even when the
thickness is very small. Thus the measuring diaphragm 56 and the
first support member 88 behave as a unit as if they were formed
integrally of the same material or Si and are capable of
suppressing the production of an output voltage due to hydrostatic
pressure.
The pressure sensing section main body 92 includes a printed base
plate 94 formed of doughnut-shaped ceramics in such a manner that
the printed base plate 94 is substantially flush with the measuring
diaphragm 56 and soldered to and supported by conductors 98
extending through a plurality of ducts 96 formed in the pressure
sensing section main body 92 on the same circumference in the
direction of the center axis. The conductors 98 are supported by a
hermetic seal 100 in the ducts 96. The printed base plate 94 is
connected to the piezo resistance elements 64-70 by conductors 102,
and the conductors 98 supported by the hermetic seal 100 are
connected to leads 104. Joined by welding to the pressure receiving
section main body 14 is a connecting metal member 110 formed with
pressure passageways 106 and 108 which in turn has the pressure
sensing section main body 92 joined thereto by welding. The
pressure sensing section main body 92 has joined thereto by welding
a plate 114 which keeps the pressure passageway 108 in
communciation with a pressure passageway 112 formed in the second
support member 90. A protective cover 116 for the printed base
plate 94 is provided between the measuring diaphragm 56 and the
pressure passageway 106. Located above the pressure sensing section
12 and connected thereto via an amplifier section main body case
118 is an amplifier section, not shown.
The high pressure side separation chamber 26 has a larger volume
then the high pressure side pressure receiving chamber 20, and the
low pressure side separation chamber 28 has a larger volume than
the low pressure side pressure receiving chamber 22. By this
arrangement, when the high pressure side seal diaphragm 16 or low
pressure side seal diphragm 18 is caused by an overload pressure to
be seated at the pressure receiving section main body 14, the
center diaphragm 24 is prevented from being seated at the pressure
receiving section main body 14. Thus the overload pressure is kept
from acting on the measuring diaphragm 56, so that deterioration of
the characteristics of the measuring diaphragm 56 and damage
thereto can be avoided.
Operation of the semiconductor pressure transducer of the aforesaid
construction will be described. When a high pressure fluid, such as
process fluid, is introduced through the high pressure fluid inlet
port 44 at the high pressure side flange 46, the pressure of the
high pressure fluid is applied through the high pressure side seal
diaphragm 16, pressure passageway 32, high pressure side separation
chamber 26 and pressure passageway 36 and 106 to one side surface
of the measuring diaphragm 56. When a low pressure fluid is led
through the low pressure fluid inlet port 48 at the low pressure
side flange 50, the pressure of the low pressure fluid is, like the
pressure of the high pressure fluid, applied through the low
pressure side seal diaphragm 18, pressure passageway 34, low
pressure side separation chamber 28 and pressure passageways 108,
112 and 120 to the other side surface of the measuring diaphragm
56. As a result, the small thickness portions 62 of the measuring
diaphragm 56 show a deflection corresponding to the pressure
differential and causes the resistance values of the piezo
resistance elements 64-70 to show a variation which is transmitted
through the conductor 102, printed base plate 94 and conductor 98
to the amplifier section to indicate the pressure differential.
When a pressure is applied to the measuring diaphragm 56, pressures
opposed in sign but substantially equal in absolute value are
applied to the piezo resistance elements 64 and 68 and 66 and 70.
At this time, the rate of change in the resistance shown by the
piezo resistance elements 64-70 can be approximated by the
following equation: ##EQU1## where .pi..sub.e : the coefficient of
vertical piezo resistance (positive);
.pi..sub.t : the coefficient of transverse piezo resistance value
(negative);
.sigma..sub.r : the radial stress; and
.sigma..sub.t : the tangential stress.
Thus the resistance elements 64 and 68 and 66 and 70 show changes
in resistance opposed in sign and substantially equal in absolute
value, thereby providing a bridge output pressure proportional to
the pressure differential.
In the embodiment shown and described hereinabove, the formation of
the oxide layer 86 and thin glass layer 84 on the first support
member 88 enables an increase in the process for working on the
measuring diaphragm 56 to be avoided and prevents a process damage
that might otherwise be caused to the piezo resistance elements.
Also, when the oxide layer and the thin glass layer are formed on
the measuring diaphragm 56, the oxide layer can concurrently serve
as a mask for etching to be done on the measuring diaphragm 56 and
it is mainly the measuring diaphragm that is worked on, so that
simplification of the production process can be obtained.
FIG. 4 is a diagrammatic representation of the results of measuring
the temperature characteristic when the bridge is subjected to
constant voltage energization. A line A represents the
characteristic obtained when the measuring diaphragm of Si of a
thickness 0.35 mm is joined to the support member of glass, and a
line B indicates the characteristic obtained when the measuring
diaphragm is joined to the support member of Si through a thin
glass layer. The characteristic represented by the line A has a
slope a and a bend b attributed to the difference in the
coefficient of thermal expansion between the measuring diaphragm of
Si and the support member of glass. The line B shows an ideal
temperature characteristic because the material used is Si for both
the measuring diaphragm and the support member and the glass layer
interposed therebetween only has a thickness of below several
.mu.m.
FIG. 5 shows the invention as incorporated in a pressure transducer
of the electrostatic capacity. A main body 200 has joined to
opposite sides thereof by welding a high pressure side and low
pressure side pressure receiving diaphragms 202 and 204 formed of
stainless steel which cooperate with the main body 200 to define
therebetween high pressure side and low pressure side pressure
receiving chambers 206 and 208 respectively. Located in the central
portion of the main body 200 is a measuring diaphragm 214
sandwiched by two support members 210 and 212 to define
therebetween high pressure side and low pressure side measuring
chambers 216 and 218 respectively. The measuring diaphragm 214 and
two support members 210 and 212 are formed of the same single
crystal silicon and an oxide layer 220 of very small thickness and
a thin glass layer 222 are interposed between the measuring
diaphragm 214 and the two support members 210 and 212. The high
pressure side pressure receiving chamber 206 and the high pressure
side measuring chamber 216 are in communication with each other
through a pressure passageway 224, and the low pressure side
pressure receiving chamber 208 and the low pressure side measuring
chamber 218 are in communication with each other through a pressure
passageway 226. The high pressure side and low pressure side
pressure receiving chambers 206 and 208, measuring chambers 216 and
218, pressure passageways 224 and 226, support members 210 and 212
and main body 200 define a space containing a silicon oil sealed
therein, and the high pressure side and the low pressure side are
separated from each other by an O-ring 228. The measuring diaphragm
214 supported by the two support members 210 and 212 produces an
output which is taken out through conductors 232, 234 and 235
hermetically sealed as indicated at 230 to outside. The pressure
transducer shown in FIG. 5 functions such that the measuring
diaphragm 214 serves as a movable electrode and the two support
members 210 and 212 serve as fixed electrodes. In this pressure
transducer, the pressure differential between the pressures of two
fluids applied to the high pressure side and low pressure side
pressure receiving diaphragms 202 and 204 causes deflection of the
measuring diaphragm 214 which is sensed as a change in
electrostatic capacity between the two support members 210 and 212
which are fixed electrodes.
From the foregoing description, it will be appreciated that
according to the invention a glass layer interposed between the
measuring diaphragm and its support member is formed on an oxide
layer. This feature enables a thin glass layer of uniform thickness
to be obtained and allows a pressure transducer to be produced
which is impervious to the influences exerted by hydrostatic
pressure and changes in temperature.
* * * * *